Method for producing an impregnated insulating tape with diagonally positioned threads and tape so produced



3,056,691 SULATING J. ZARTL METHOD FOR PRODUCING AN IMPREGNATED IN Oct. 2, 1962 TAPE WITH DIAGONALLY POSITIONED THREADS AND TAPE SO PRODUCED Filed June 4. 1959 INVENTOR: JOSEF zART L,

H/S HTTORNEX @ZC/4m; Si

nite States aussen son recuperare AN ratrnnnnnrnn The invention relates to impregnated insulating tape, of the type that has diagonally positioned threads, which is commonly used in the electric industry. The invention further relates to methods of producing such tape, and to a seamless tape of this type.

lt is among the principal objects of the invention to provide and to produce an impregnated insulating tape with diagonally positioned threads, which product and process are simple, inexpensive and reliable.

Further objects and advantages of the invention will be set forth in part in the following specification and in part will be obvious therefrom without being specifically referred to, the same being realized and attained as pointed out in the claims hereof.

With the above and other objects of the invention in View, the invention consists in the novel methods, construction, arrangement and combination, as set forth in the claims hereof, one embodiment of the same being described in this specification.

impregnated insulating tapes with diagonally positioned threads have, in the past, been produced according to one of the following two methods. According to the first known method, a web of linen fabric is insulated with an insulating lacquer. Parallelograms are cut from the web, and the original edges of the web, this time having diagonally positioned threads are joined together to form a new web. The joining is either by sewing or by cementing. Subsequently, the new web is cut into tape on a tape cutting machine.

Tapes produced in this manner have the disadvantage that the cemented or sewn portions have at least twice the thickness of the other portions and are far less resistant to stresses as compared to the remaining portions. Furthermore, the sewing or cementing of the diagonal webs is time-consuming and costly.

In accordance with the second method of the prior art, a tubular fabric is cut into strips in accordance with the desired diagonal angle. The cut strips are thereafter impregnated with an insulating lacquer.

This method gives rise, however, to a series of difficulties. Por instance, the strips do not possess in the longitudinal direction (of the diagonal web) a suflicient strength against stresses; if they are subjected to stresses in the direction of their length, which is inevitable during reeling, the strips Will be distorted and be rendered useless for further treatment. Attempts have been made to remedy this drawback by subjecting the strips, prior to the impregnating, to a finishing or dressing operation while subjectinf it to lateral stretching, endeavoring to impart to the strips a greater strength against stresses. This preliminary operation, however, is costly and complicated, particularly as the finishing or dressing step usually needs to be applied in a separate finishing or dressing plant. The finishing or dressing furthermore is detrimental for the subsequent step of absorption of the insufice lating material, as the finishing or dressing step reduces the absorption quality of the strip. Moreover, the final tape will be composed not only of fabric and insulating lacquer but also will contain up to ten percent of nishing or dressing material, which has the disadvantage that the resistance of the tape to heat may be considerably less than needed.

in the accompanying drawings, described in detail below,

FIG. 1 is a schematic View showing a How sheet;

PEG. 2 is a fragmentary perspective view of a tubular fabric in accordance with the invention; and

FIG. 3 is a fragmentary perspective View of a tape cut from the fabric.

The invention aims at obviating the difficulties of the prior art. Broadly speaking, the instant invention provides for a pre-irnpregnation step (at b, FIG. l) in which the tubular fabric is treated, prior to the cutting thereof into strips (at c, FIG. l), in a bath with a thin solution of an impregnating liquid, followed by a drying step. The liquid of the pre-impregnation solution will have the same or similar chemical properties as the main impregnating solution, but will have a smaller concentration. The concentration of the solution of the aforesaid preimpregnating bath is selected in such a manner that the tubular fabric will be stiffened but will not in the subsequent drying step cause adhesion among any of its parts. After the drying, the tubular fabric 11 is cut into strips 12 in accordance with the desired diagonal (helical) angle along cutting lines 13. The strips 12 cut from the stiffened tubular fabric need to have sufficient strength and rigidity so that the edges will not roll up and the fabric will not be deformed or disintegrate.y during the subsequent treatment in which the strips are stressed longitudinally. The pre-impregnation with the thin solution should penetrate into the interior of the fabric, but should not close the pores along the surface of the fabric, as otherwise the surface would be tacky and its absorption for the second, the main impregnation, step at d, FIG. l) would be diminished or lost. In accordance with the invention, the concentration of the pre-impregnating solution is less than one-half of the concentration of the main impregnating solution.

The impregnating substance may for instance be insulating lacquer in organic solvents. The pre-impregnating substance may be the same or similar laquer; the preimpregnating solution will then differ from the main irnpregnating solution mainly by its smaller concentration. instead of insulating lacquers, there may be used oil lacquers or solutions of plastic material or synthetic resins; if these substances are used, the concentration of the pre-impregnating solution may be from 5 to 2G percent, and the concentration of the main impregnating solution from 20 to 40 percent.

After the strips 12 have been cut from the pre-impregnated tubular fabric 11, they have their threads 14 positioned diagonally. The strips are drawn through a bath of the main impregnating solution, and then are dried. Thereafter, the impregnated strips 12 are cut (at e, FIG. l) into tapes 15 on a cutting machine, and are rolled up.

The tapes 15 produced in this manner .are seamless and are characterized by uniform mechanical and electrical qualities. These qualities are better than those of tapes heretofore made, and yet the instant tapes are less expensive to produce.

During the manufacture of the fabric itself, there is added a sizing material to improve the working with the fabric on the loom. The sizing material, however, is added in extremely small quantities, for instance of from .0l to .05 of one percent. r[This small addition does not affect adversely the heat resistance of the final tape product; in contrast thereto, the aforesaid high percentage (up to l() percent) of the nishing or dressing operation under the prior art materially reduces the heat resistance of the tape. In order to make insulating tape resistant to extremely high temperatures, there may be employed a preliminary burning step during which the sizing material becomes volatile and evaporates.

The tape made in accordance ywith the invention is composed solely of the fabric and insulating medium such as insulating lacquer. `Instead of solutions, there may be employed emulsions or dispersions yielding a similar result.

Examples I. A tube of r-ayon fabric of a width of 67 cm. and a thickness of .O8 mm., is pre-impregnated with a l3 percent oil lacquer, and is thereafter dried in a drying tower. Subsequently, the tube is cut helically at an angle of 20 to the warp. The diagonal strip then will have a width of about 130 centimeters, and is thereafter subjected twice in succession to an impregnating step with a 25 to 30 percent oil lacquer solution; after each impregnation, the strip is dried. The resulting insulating diagonal strip has a thickness of .15 mm. It is thereafter cut on a cutting machine into tapes.

II. A tube made of glass silk fabric with a thickness of .05 mm., is impregnated with a 7 percent Desmodur- Desmophen solution. Desmodur-Desmophen lacquer solutions are well known and are prepared from a mixture of polyurethane (Desmodur) and polyester (Des4 mophen), a typical example of these lacquers being the following:

100 parts Desmophen 2200 from Bayer AG, Leverkusen (adipic acid-ethylene glycol polyester with hydroxyl number of 50-60) l5 parts toluene di-isocyanate (Desmodur T) These ingredients are mixed in 7% solution (resin solids) in organic solvent containing toluene, ethyl acetate and methyl glycol acetate. The degree of network of the preimpregnation by this solution is smaller than that at the subsequent main impregnation. The tube will thereafter be cut at an angle of 45 relative to the direction of the warp, and the resultant diagonal strips will then 4be treated in a bath to ybe impregnated once, with a 20 percent solution, and thereafter are hardened in a drying tower. The final strip will have a thickness of .O8 nim.; finally, it will be cut into tapes.

III. A tube of fabric made of polyester fiber (for instance known under the trademark Terylen) of .03 mm, thickness, is pre-impregnated with a percent solution of Athoxylin resin in accordance wit-h Example I. Athoxylin resin solution is a Well known insulating resin varnish and is based upon the condensation resin product from the reaction of epichlorhydrin and bis phenol. These products known under this name as furnished by Ciba AG, Basel, Switzerland, are furnished in toluene as solvent and contain l0() parts of epoxy resin (condensation product of bis phenol and epichlorhydrin), 100 parts of polyamine hardener. Thereafter, it is cut, and the strips subjected to a main impregnation of a 30 percent solution of Athoxylin resin and will have in the end a thickness of .08 mm. .From the strip the tapes will be cut.

IV. A fabric made of natural silk is treated with a solu` tion of alkyd resin or of a polyester resin, in accordance with the teachings of Example II.

V. A tube made of glass silk fabric is treated with modil lied or unmodified silicon resins, in accordance with the step sequence of Examples I or II.

VI. A tube of glass silk fabric is treated with dispersions or solutions of triuoromonochlorethylene (for instance, of the type known under the trademark Hostaflon), in accordance with the step sequence of Examples I or II.

VII. A tubular fabric of polyamid fiber (for instance, known under the trademark Perlon) is treated with modified melamine resins or urea resins, in a step sequence of Examples I or II.

VIII. A tubular fabric of cotton or wool is treated in accordance with Example II with polyvinyl derivatives, in solution, emulsion or dispersion.

IX. A tubular fabric of asbestos is treated with natural or synthetic rubber or rubber derivatives, in a step sequence of Examples I or II.

It will be understood by the skilled artisans that the tube of each of the aforesaid examples may alternatively be used with the impregnating materials of 'any other of the examples.

I wish it to be understood that I do not desire to be limited yto the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the fart.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows:

l. In a method of producing from la tubular fabric irnpregnated insulating tapes with diagonally positioned threads, the steps comprising, pre-impregnating said tube with `an insulating resinous lacquer by dipping said tube in a bath containing said lacquer, the lacquer solids in said lacquer being less than about one-half of the concentration of that used to provide a final stiffened insulating tape `and providing a concentration of lacquer which after drying imparts sufhcient strength yand rigidity to prevent rolling up of the edges and deforming of the fabric under longitudinal stress, said concentration also penetrating the interior of the fabric without closing the pores thereof and thereafter drying said tube, subsequently cutting said tube helically into strips, and thereafter subjecting the strips to a main impregnation step in a bath with a lacquer having a higher concentration of lacquer solids than the said pre-impregnating solution, the lacquer solids being the same as in the pre-impregnating solution, said higher concentration of lacquer solids being in the range of 20 to 40 percent.

2. In a method as claimed in claim 1, the pre-impregnating lacquer having a concentration of 5 to 20' percent.

3. In a method as claimed in claim l, said cutting of the tube helically into strips taking place at an acute angle to the fabric warp, the pre-impregnating lacquer being sufficiently thinner than the main impregnating lacquer so as to restrain closing of the pores of the fabric Surface leaving the fabric sufficiently absorptive for the absorption during the subsequent main impregnating.

4. In a method of producing from a 4tubular fabric impregnated insulating tapes with diagonally positioned threads, the steps comprising, pre-impregnating said tube with a diluted solution of an impregnating substance selected from the group consisting of oil lacquer, natural resins, and synthetic resins, by Idipping said tube in a bath containing said diluted solution, the solids in said solution being less than about one-lialf of the concentration of that used to provide a final stiffened insulating tape and providing a concentration of solution which after drying imparts sufficient strength and rigidity to restrain rolling up of the edges and deforming of the fabric under longitudinal stress, said concentration also penetrating the interior of the fabric without closing the pores thereof lan-d thereafter drying said tube, subsequently cutting said tube helically into strips, and thereafter subjecting the strips to a main impregnation step in a bath with Ia solution of said impregnating substance having a higher concentration of solids than the said predmpregnating solution, said higher concentration of solids being in the range of from 20 to 40 percent.

5. In a method as claimed in claim 4, the pre-impregnating solution having `a concentration of 5 to 2O` percent.

6. In 1a method as claimed in claim 4, said cutting of the tube helically into strips taking place at yan acute angle to the fabric warp, the pre-impregnating solution being sufficiently thinner than the matin impregnating solution so as to restrain closing of the pores of the fabric surface leaving the fabric suiciently absorptive for the absorption during the subsequent main impregnating.

7. An insulating fabric tape with diagonally positioned threads made and impregnated in laccordance with the method of claim 4.

References Cited in the le of this patent UNITED STATES PATENTS 602,797 Annison Apr. 19, 1898 1,857,690 Mellanoff May 10, 1932 2,355,038 Barnard Aug. 1, 1944 2,879,581 Evans et al. Mar. 31, 1959 2,953,477 Evans Sept. 20, 1960 

4. IN A METHOD OF PRODUCING FROM A TUBULAR FABRIC IMPREGNATED INSULATING TAPES WITH DIAGONALLY POSITIONED THREADS, THE STEPS COMPRISING, PRE-IMPREGNATING SAID TUBE WITH A DILUTED SOLUTION OF AN IMPREGNATING SUBSTANCE SELECTED FROM THE GROUP CONSISITN OF OIL LACQUER, NATURAL RESINS, AND SYNTHETIC RESINS, BY DIPPING SAID TUBE IN A BATH CONTAIING SAID DILUTED SOLUTION, THE SOLIDS IN SAID SOLUTION BEING LESS THAN ABOUT ONE-HALF OF THE CONCENTRATION OF THAT USED TO PROVIDE A FINAL STIFFENED INSULATING TAPE AND PROVIDING A CONCENTRATION OF SOLUTION WHICH AFTER DRYING IMPARTS SUFFICIENT STRENGTH AND RIGIDITY TO RESTRAIN ROLLING UP OF THE EDGES AND DEFORMING OF THE FABRIC UNDER LONGITUDINAL STRESS, SAID CONCENTRATION ALSO 